Hydride-Mediated Hydrogen Activation on Cobalt-Alloyed Single-Atom Palladium Catalysts for Efficient H₂O₂ Synthesis

Single-atom catalysts (SACs) exhibit excellent performance in a range of hydrogenation reactions. However, the mechanistic understanding of hydrogen intermediates formed following H₂ dissociation, particularly their reactivity on SAC surfaces, remains limited. In this study, we show that single-atom palladium alloyed with cobalt (Pd₁Co SACs) efficiently catalyzes the hydrogenation of anthraquinone, exhibiting high stability and recyclability. In contrast, a cobalt oxide-supported Pd single-atom catalyst (Pd₁-Co₃O₄) displays only limited activity. Experimental results indicate hydrogen dissociation as the rate-determining step in the anthraquinone hydrogenation process. Density functional theory calculations reveal that Pd₁Co SACs enable homolytic H₂ dissociation with a low activation energy and facilitate electron transfer from the support to the hydrogen intermediates, resulting in the formation of highly reactive hydride-like species. The combination of high atomic efficiency and low energy barrier enables Pd₁Co SACs to achieve a remarkable H₂O₂ production rate of up to 210 mol g_Pd^-1 h^-1, which is 240 times greater than that of commercial Pd/Al₂O₃.